<html>
    <head>
      <base href="https://bugs.webkit.org/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - WebKit incorrectly clips position:fixed element, inside of its &quot;position:relative; overflow: hidden&quot; parent, IF that parent has &quot;z-index&quot; set"
   href="https://bugs.webkit.org/show_bug.cgi?id=160953">160953</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>WebKit incorrectly clips position:fixed element, inside of its &quot;position:relative; overflow: hidden&quot; parent, IF that parent has &quot;z-index&quot; set
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>WebKit
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>Safari 9
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>Normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P2
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Layout and Rendering
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>webkit-unassigned&#64;lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>dholbert&#64;mozilla.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>simon.fraser&#64;apple.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>STR:
 1. Load this testcase: <a href="https://jsfiddle.net/bo4q2hbh/">https://jsfiddle.net/bo4q2hbh/</a>

EXPECTED RESULTS:
 Teal div should not be clipped at orange border. (The teal div is a fixed-position element, and it should use the viewport as its containing block, rather than using its orange-bordered relpos ancestor.)

ACTUAL RESULTS:
 Teal div is clipped at orange border! (in Safari)

I get EXPECTED RESULTS in Firefox 48, Edge 14, and Chrome 54.
I get ACTUAL RESULTS in Safari 9.1 (on Mac OS El Capitan)

The bug only happens if the relatively-positioned ancestor has &quot;z-index&quot; set.  In my above-linked jsfiddle, that element has &quot;z-index: 0&quot;. If I remove that line, the bug goes away and I end up with EXPECTED RESULTS.

Note: Chrome has a similar bug, but their bug is more restricted (it only happens if there's also 3d-transformed descendant).
<a href="https://bugs.chromium.org/p/chromium/issues/detail?id=638780">https://bugs.chromium.org/p/chromium/issues/detail?id=638780</a></pre>
        </div>
      </p>
      <hr>
      <span>You are receiving this mail because:</span>
      
      <ul>
          <li>You are the assignee for the bug.</li>
      </ul>
    </body>
</html>